1. Field of the Invention
The invention relates to a circuit arrangement with an odd number of converters and, in particular, with an odd number m of direct frequency converters.
2. Description of the Prior Art
A circuit arrangement is known in which a number of direct frequency converters are connected in a symmetrical Y-connection to a symmetrical m-phase load without a direct connection between the neutral point of the frequency converters and the neutral point of the load. In this circuit arrangement, the conductor voltages at the load each have a predetermined periodic waveform and together form a symmetrical system. More particularly, in such circuit arrangement control voltages are coupled into control units of the m frequency converters in such a manner that the output voltages of the converters have substantially a trapezoidal waveform.
If, in this circuit arrangement, a current regulator were associated with each converter and the arrangement were operated with the neutral point of the load open, then the output voltages of the current regulators, which voltages serve as the control voltages for the control units of the converters, would be divergent, as the regulators would have an integral component in their time behavior. The reason for this is that with the neutral point of the load open, the sum of all phase currents must be equal to zero.